Fix partial cloning a repo (go-gitea#18373)

- Backport from: go-gitea#18373
- Backport isn't 1-1, because the frontport had a refactor in that area,
which v1.16 doesn't have.

routers/web/repo/http.go

@@ -494,6 +494,7 @@ func serviceRPC(h serviceHandler, service string) {
 	cmd := exec.CommandContext(ctx, git.GitExecutable, service, "--stateless-rpc", h.dir)
 	cmd.Dir = h.dir
 	cmd.Env = append(os.Environ(), h.environ...)
+	cmd.Env = append(cmd.Env, git.GlobalCommandArgs...)
 	cmd.Stdout = h.w
 	cmd.Stdin = reqBody
 	cmd.Stderr = &stderr